In recent years, as a so-called keyless entry system, there are proposed various systems enabling locking/unlocking of a vehicle or the like by operating a mobile phone, in place of using a key-holder or a key. For instance, Patent Literature 1 proposes a system, in which locking/unlocking a vehicle is performed or various operations of vehicle-mounted devices are performed by causing a center to communicate with the vehicle-mounted devices on the basis of an operation of a mobile phone. Further, Patent Literature 2 proposes a mobile phone such that a transmitter or a control circuit for locking/unlocking is incorporated in a phone body, and locking/unlocking a vehicle is performed by directly transmitting a signal from the mobile phone to the vehicle according to an operation of the mobile phone.
In a system using a communication line of a mobile phone as disclosed in Patent Literature 1, however, a development cost rises, and a communication fee or the like is also involved. Therefore, it is difficult to provide an inexpensive system. Further, in the case of Patent Literature 2, in addition to the necessity of newly developing a mobile phone itself, the degree of freedom in selecting a mobile phone by the user may be narrowed, because the mobile phone is used as a dedicated device for a vehicle. In view of the above, in recent years, there is proposed an idea that a keyless entry function is substantially provided in a mobile phone by loading a transmitter or an operation button for locking/unlocking on a cover for the mobile phone (especially, a cover for a smartphone). According to this configuration, it is possible to provide a mobile phone with a keyless entry function with a simplified and inexpensive configuration without impairing the degree of freedom in selecting a mobile phone by the user.
When a transmitter or an operation button for locking/unlocking is provided in a cover for a mobile phone, however, there may occur an erroneous operation e.g. a case in which the operation button provided on the cover is pressed against the user's intention during an operation of the mobile phone, and the vehicle may be locked/unlocked. Therefore, it is necessary to prevent such an erroneous operation.